1. Field of the Invention
The present invention relates to detecting defective printing systems and, more particularly in certain embodiments, to detecting defective ink jet nozzles in a postage indicia printing system.
2. Brief Description of Background
Currently there is no way for a postage meter to determine if a particular ink jet nozzle or group of nozzles is failing in a postage meter using ink jet printing technology. Certain postal systems require that postage indicia include a two-dimensional barcode for encoding postage indicia information that may then be read and decoded by automated postal processing equipment. Accordingly, many postage meters print postage indicia using linear ink jet arrays of a particular width such as one inch. Furthermore, postal systems are increasingly using two-dimensional barcodes to transmit additional data such as information relating to value added services stored in a second barcode. Therefore, it is becoming more important in the mailing industry that barcodes be readable to a high degree of accuracy because the postal systems are using them with value added services and revenue protection schemes.
Two-dimensional bar codes utilize a defined encoding format having certain known absolute or relative physical formatting rules and symbologies so that bar code readers can read the bar code so that the embedded information may be decoded. There are many standard Two-dimensional bar codes formats including the DATAMATRIX bar code that have some error checking and redundancy, but may also have regions that are more vulnerable to failure. For example, the DATAMATRIX bar code format includes an “L finder” region and a “timing pattern” region that may be more sensitive to failures than data regions of the bar code. A single damaged or missing ink-jet nozzle that is located in an area that prints a sensitive region such as the “timing pattern” region may disproportionately negatively affect the accurate readability of the postage meter. Accordingly, the printed indicia might not be readable and may result in a loss of postage funds or other negative consequence such as late delivery of the mail.
Certain high-speed mailing machines with postage meters such as the TURBOJET available from Pitney Bowes Inc. of Stamford Conn. print postage indicia at a relatively high rate of speed. If there is an ink-jet nozzle failure in a critical location, it is possible that $50,000 worth of postage could be lost per hour. It is possible to create an ink-jet postage meter indicia error detection system that reads the entire bar code, decodes the information and then compares the read information with the expected written information to determine if there has been a printing failure. However, such a system would scan an image of the full bar code or mailpiece to determine if there is a defect in the printed image. Such a system would require relatively significant computing power and expensive imaging and decoding software/hardware.
Accordingly, there is a need for a relatively inexpensive and fast ink-jet nozzle failure detection system. Furthermore, there is a need for a relatively inexpensive and fast ink-jet nozzle failure detection system for detecting failed nozzles in a sensitive region of the ink-jet nozzle array.